The invention relates to a double helix comprising two helix elements made of plastic wire with the longitudinal axes of the two helix elements extending in parallel, to the production of such helices in which two plastic wires are wound on a mandrel, and to the use of the double helices to produce a spiral belt of the type wherein the helices are engaged with their windings in zipper fashion and are secured by a pintle wire.
Spiral belts comprised of helices are used as conveyor belts and as papermachine clothing. The costs involved in the manufacture of such belts are highly dependent on the production costs of the helices. Likewise, the production capacity of the belts depends primarily on that of the helices. In general, the production capacity of a machine assembling the helices to form a spiral belt is so high that a great number of helix producing machines operating at maximum speed are required to feed the assembling machine. Therefore, to minimize the helix production costs, it is essential that the output of the individual helix making machines be maximized.
The capacity of a helix producing machine can be increased by winding double helices instead of a single helix element. A double helix and a method for producing same are known from German Auslegeschrift No. 2,003,344. In this method, the two helix elements of the double helix are readily separated by laterally pulling the helices apart. This is accomplished by a complicated method in which the two helix wires are wound on a mandrel so as to alternately cross each other. Owing to these crossings, however, the helices have an asymmetrical cross section which makes them unsuited for the assembly of spiral belts having a smooth surface. Moreover, this reference fails to describe how the helices can be further processed to form a screen belt. Double helices have also been known from European patent application No. 18200. However, the double helices disclosed in this application are used with their longitudinal axes congruent i.e., without lateral displacement.
Spiral belts assembled from a multiplicity of helices in which the windings of the individual helices are intertwined are disclosed in German Pat. Nos. 54,525, 77,147 and 80,763. In these belts, pintle wires can be additionally inserted between the entwined windings. However, assembly of these belts from single helix structures requires that each new helix be screwed into the preceding helix. Such spiral belts are thus far more expensive to produce than are the spiral belts disclosed, for example, in German OS No. 2,938,221 where the helices mesh normal to their longitudinal axes and are secured in position by pintle wires.
It is therefore a primary object of the present invention to reduce the overall costs of producing spiral belts by reducing the cost factor of helix production.